基于改进格林元的压裂水平井动态分析方法

Transient Behavior Analysis of Fractured Horizontal Wells Based on an Improved Green Element Method

以建立高效的动态分析方法为出发点,以边单元作为求解点,改进传统的格林元方法,减少未知数和求解矩阵维度;并提出基于改进格林元的加密网格加密方法,保证考虑复杂裂缝网络的压裂水平井动态模拟的早期精度.退化模型与半解析解、数值模拟结果进行对比,验证本文基于加密网格的改进格林元方法的准确性和动态分析的高效性.最后进行动态响应的敏感性分析,结果表明:①格林元方法是一种高精度的动态模拟方法,将求解节点设置在网格的边上可以提高压裂水平井动态模拟的速度;②改进格林元方法的加密基于叠加原理,不需要通过插值近似,其求解精度高.在相同加密网格条件下,基于本文改进格林元方法的加密效果比有限差分加密效果更佳;③复杂裂缝导流能力、改造区渗透率提高倍数、改造区大小等参数对压裂水平井动态特征影响较大,在动态分析和参数反演时,应着重考虑这些因素的影响.

We proposed a modified Green element method based on edge-based element concept.Unknowns and matrix dimension are reduced.Then,a local grid refinement method is proposed based on the improved Green element,which ensures precision in early flow regimes for fractured horizontal wells with complex fractured networks.Solution of a degradation model solved with the method is compared with solutions obtained with a semianalytical model and numerical simulation.It verifies accuracy and efficiency of the improved Green element method based on local grid refinement.Finally,effects of model parameters on transient behavior is analyzed.It shows that the Green element method is a high precision dynamic simulation method,which improves computational efficiency of dynamic simulation of fractured horizontal well by setting node on edge of grid.In addition,local grid refinement method applied to the modified Green element method is based on superposition principle,in which interpolation approximation is not needed.The method is of high accuracy.Under same grid systems,local grid refinement based on improved Green element method is better than using finite difference.On the other hand,conductivity of complex fracture,permeability and size of stimulated reservoir volume have great influence on transient behavior of fractured horizontal wells.These effects should be taken into consideration and interpreted in transient behavior analysis.